In printing, there are numerous ways of transferring the ink to a substrate on which to print. One of these methods is flexographic printing, which is a process that uses rubber or another suitable material as a printing plate carried on a cylinder, to convey the image to the substrate, such as a corrugated board. There are several methods of getting the ink from its supply, such as a fountain, to the printing plate and ensuring delivery of the proper amount of ink.
One of the most common methods of ink delivery is to use an anilox roll. The anilox roll is flexible and has numerous small cells to hold the ink. The number of cells can vary from 30,000 to 300,000 cells per square inch. The anilox roll with ink transfers the ink to the printing plate. There are two common style machines or methods to fill the cells of the anilox roll and properly meter the ink. The two methods are using a doctor blade in conjunction with the anilox roll and using a wiper roll in conjunction with the anilox roll. This second style machine or method is sometimes referred to as two (2) roll inking or metering system.
The invention relates to a machine that uses the wiper roll to meter the ink to the anilox roll. Therefore, the prior art of this style of machine and method will be discussed in further detail. The anilox roll and the wiper roll form a nip created by the contact of these rolls together. This nip and the rolls form a trough which acts as an ink fountain. The contact force between the wiper roll and the anilox roll determines the amount of ink film which remains in the cells and on the anilox roll. This ink will be transferred to the printing plate. The minimum contact force occurs when the wiper roll just touches or "kisses" the surface of the anilox roll with enough force to form the nip and hold ink.
It has been recognized that to adjust the contact force, the wiper roll is mounted eccentrically in a housing relative to a frame. Rotation of the housing in the frame results in translational movement of the wiper roll relative to the anilox roll. The operator rotates a mechanical adjusting mechanism, such as a wrench, coupled to a gear engaging a rack on the housing in order to rotate the housing. The rotation moves the wiper roll translationally into or out of contact with the anilox roll. This movement is typically called the opening or closing of the wiper to the anilox roll. With this manual system, the operator could "feel" when the rolls initially make contact. The minimum contact force is defined as the "zero position."
One of the reasons for eccentrically mounting the wiper roll, is that the wiper roll in a flexo ink system has an elastic-type covering, such as rubber or another synthetic material, which is subject to wear. A worn roll can be removed from the ink fountain and refinished to produce a smoother wiping surface. However, this refinishing process reduces the diameter of the roll. In addition, the normal wear of the wiper roll from running the machine reduces the diameter of the wiper roll. Therefore, the center or longitudinal axis of the wiper roll needs to be adjusted in order to get the proper contact force.
While an operator with years of experience can tell by the resistance of the wrench that the wiper roll is in proper position therein giving the proper mount of contact force between rolls, it is desired to replace the manual movement by an automatic process so as to increase automation and speed production allowing the operator to perform other functions.
However, the automatic process does not have the benefit of the operator feeling the contact. Moreover, the contact torque cannot be adequately determined using feedback methods. It is therefore desired to have an apparatus for and a method of loading the wiper roll against the anilox roll wherein the "zero position" can be determined reliably and mechanically.